Add dataSourceChanged signal to QgsVectorLayer, add tests

python/core/auto_generated/qgsvectorlayer.sip.in

@@ -986,6 +986,8 @@ if the geometry type of the new data source matches the current geometry type of
 :param loadDefaultStyleFlag: set to true to reset the layer's style to the default for the
                              data source
 
+.. seealso:: :py:func:`dataSourceChanged`
+
 .. versionadded:: 3.2
 %End
 
@@ -2295,6 +2297,15 @@ by the backend data provider).
 
   signals:
 
+    void dataSourceChanged();
+%Docstring
+Emitted whenever the layer's data source has been changed.
+
+.. seealso:: :py:func:`setDataSource`
+
+.. versionadded:: 3.4
+%End
+
     void selectionChanged( const QgsFeatureIds &selected, const QgsFeatureIds &deselected, bool clearAndSelect );
 %Docstring
 This signal is emitted when selection was changed

src/core/qgsvectorlayer.cpp

@@ -1482,7 +1482,10 @@ void QgsVectorLayer::setDataSource( const QString &dataSource, const QString &ba
   setDataProvider( provider, options );
 
   if ( !mValid )
+  {
+    emit dataSourceChanged();
     return;
+  }
 
   // Always set crs
   setCoordinateSystem();
@@ -1520,6 +1523,7 @@ void QgsVectorLayer::setDataSource( const QString &dataSource, const QString &ba
     setLegend( QgsMapLayerLegend::defaultVectorLegend( this ) );
   }
 
+  emit dataSourceChanged();
   emit repaintRequested();
 }
 

src/core/qgsvectorlayer.h

@@ -964,6 +964,7 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionConte
      * \param options provider options
      * \param loadDefaultStyleFlag set to true to reset the layer's style to the default for the
      * data source
+     * \see dataSourceChanged()
      * \since QGIS 3.2
      */
     void setDataSource( const QString &dataSource, const QString &baseName, const QString &provider, const QgsDataProvider::ProviderOptions &options, bool loadDefaultStyleFlag = false );
@@ -2062,6 +2063,15 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionConte
 
   signals:
 
+    /**
+     * Emitted whenever the layer's data source has been changed.
+     *
+     * \see setDataSource()
+     *
+     * \since QGIS 3.4
+     */
+    void dataSourceChanged();
+
     /**
      * This signal is emitted when selection was changed
      *

tests/src/python/test_qgsvectorlayer.py

@@ -22,6 +22,7 @@ from qgis.PyQt.QtXml import QDomDocument
 
 from qgis.core import (QgsWkbTypes,
                        QgsAction,
+                       QgsDataProvider,
                        QgsDefaultValue,
                        QgsEditorWidgetSetup,
                        QgsVectorLayer,
@@ -60,6 +61,7 @@ from qgis.core import (QgsWkbTypes,
 from qgis.gui import (QgsAttributeTableModel,
                       QgsGui
                       )
+from qgis.PyQt.QtTest import QSignalSpy
 from qgis.testing import start_app, unittest
 from featuresourcetestbase import FeatureSourceTestCase
 from utilities import unitTestDataPath
@@ -292,6 +294,48 @@ class TestQgsVectorLayer(unittest.TestCase, FeatureSourceTestCase):
         self.assertEqual(layer.undoStack().index(), 2)
         self.assertEqual(layer.featureCount(), 4)
 
+    def testSetDataSource(self):
+        """
+        Test changing a layer's data source
+        """
+        layer = createLayerWithOnePoint()
+        layer.setCrs(QgsCoordinateReferenceSystem("epsg:3111"))
+        r = QgsSingleSymbolRenderer(QgsSymbol.defaultSymbol(QgsWkbTypes.PointGeometry))
+        layer.setRenderer(r)
+        self.assertEqual(layer.renderer().symbol().type(), QgsSymbol.Marker)
+
+        spy = QSignalSpy(layer.dataSourceChanged)
+
+        options = QgsDataProvider.ProviderOptions()
+        # change with layer of same type
+        points_path = os.path.join(unitTestDataPath(), 'points.shp')
+        layer.setDataSource(points_path, 'new name', 'ogr', options)
+
+        self.assertTrue(layer.isValid())
+        self.assertEqual(layer.name(), 'new name')
+        self.assertEqual(layer.wkbType(), QgsWkbTypes.Point)
+        self.assertEqual(layer.crs().authid(), 'EPSG:4326')
+        self.assertIn(points_path, layer.dataProvider().dataSourceUri())
+        self.assertEqual(len(spy), 1)
+
+        # should have kept the same renderer!
+        self.assertEqual(layer.renderer(), r)
+
+        # layer with different type
+        lines_path = os.path.join(unitTestDataPath(), 'lines.shp')
+        layer.setDataSource(lines_path, 'new name2', 'ogr', options)
+
+        self.assertTrue(layer.isValid())
+        self.assertEqual(layer.name(), 'new name2')
+        self.assertEqual(layer.wkbType(), QgsWkbTypes.MultiLineString)
+        self.assertEqual(layer.crs().authid(), 'EPSG:4326')
+        self.assertIn(lines_path, layer.dataProvider().dataSourceUri())
+        self.assertEqual(len(spy), 2)
+
+        # should have reset renderer!
+        self.assertNotEqual(layer.renderer(), r)
+        self.assertEqual(layer.renderer().symbol().type(), QgsSymbol.Line)
+
     # ADD FEATURE
 
     def test_AddFeature(self):